oops, sorry Chain Saw...you asked the question fine, i just took it wrong.
Whenever there is a vacancy in the office of the Vice President, the President shall nominate a Vice President who shall take office upon confirmation by a majority vote of both Houses of Congress.")
If for some reason there is no President or Vice President, the Speaker of the House will become President (the Speaker then ceases to be a Representative). If for some reason the Speaker cannot serve, then the President pro tempore of the Senate will.
If the President pro tempore cannot serve, then the following succession will apply: Secretary of State, Secretary of the Treasury, Secretary of Defense, Attorney General, Secretary of the Interior, Secretary of Agriculture, Secretary of Commerce, Secretary of Labor, Secretary of Health and Human Services, Secretary of Housing and Urban Development, Secretary of Transportation, Secretary of Energy, Secretary of Education, Secretary of Veterans Affairs.